Preliminary analysis of the zonal distribution of ENSO-related SSTA in three CMIP5 coupled models

• Main Authors: Zi-an GE, Lin CHEN
• Format: Article
• Language: English
• Published: KeAi Communications Co., Ltd. 2020-09-01
• Series: Atmospheric and Oceanic Science Letters
• Subjects: enso; ssta zonal distribution; coupled models; simulation bias
• Online Access: http://dx.doi.org/10.1080/16742834.2020.1775475

The simulated sea surface temperature anomaly (SSTA) over the tropical Pacific during El Niño–Southern Oscillation (ENSO) is investigated in three representative coupled models: CESM1-CAM5, FGOALS-s2, and FGOALS-g2. It is found that there is a significant westward shift bias in reproducing the zonal distribution (ZD) of the ENSO-related SSTA in CESM1-CAM5 and FGOALS-s2, whereas the SSTA-ZD simulated by FGOALS-g2 is relatively realistic. Through examining the SSTA-ZD during both warm and cold phases of ENSO separately, the authors reveal that the SSTA-ZD simulation bias during the ENSO cycle mainly lies in the bias during the warm phase. It is noted that both the simulated zonal wind stress anomaly ($$\tau _x^'$$) and shortwave heat flux (SW) anomaly exhibit westward shift biases in CESM1-CAM5 and FGOALS-s2, while the counterparts in FGOALS-g2 are relatively reasonable. The westward shift biases in representing $$\tau _x^'$$ and the SW anomaly (SWA) are attributed to the westward-shifted precipitation anomaly (PrA). It is suggested that the mean SST cold bias over the cold tongue region is the key factor behind the westward-shift bias in simulating the El Niño-related PrA, which leads to the westward-shifted $$\tau _x^'$$ and SWA. Collectively, the aforementioned anomaly fields, including the dynamic part ($$\tau _x^'$$) and thermodynamic part (SWA), contribute to the westward-shift bias in simulating the El Niño-related SSTA. This study provides clues for understanding the ZD simulation biases of ENSO-related fields; however, further in-depth investigation with more model simulations, especially the incoming CMIP6 simulations, is still needed to fully understand the ENSO SSTA-ZD simulation bias in coupled models.